Gas burner

ABSTRACT

A gas burner of the type having a blast tube and a blower for supplying air to the blast tube adjacent its rear end. A gas and air mixing tube is longitudinally supported in the blast tube with its forward end spaced rearwardly from the forward end of the blast tube, and a nozzle injects gas into the rear end of the mixing tube. The mixing tube has an air inlet opening adjacent its rear end for admitting primary air thereto for forward flow therein and mixture with the gas, the secondary air flowing forwardly over and around the mixing tube. The relationship of the primary and secondary airflow is controlled by a gate for selectively varying the area of the air inlet opening in the mixing tube. A burner drum is mounted in the forward end of the blast tube by a partition extending between the rear end of the drum and the forward end of the mixing tube, the drum extending longitudinally forwardly from the partition with its forward end spaced rearwardly from the forward end of the blast tube, the secondary air flowing forwardly over and around the drum and a flame being formed within the drum upon ignition of the fuel-air mixture exiting from the mixing tube. The drum has elongated, circumferentially extending slots formed in its wall forwardly of the mixing tube so that the secondary air flowing forwardly over the drum and the slots creates a partial vacuum adjacent the inner surface of the drum wall so as to spread the flame in the drum.

tates Patent box [ GAS BUNER [72] Inventor: Paul D. Cox, Ridgeville, Ind.

[73] Assignee: Cox Manufacturing Co., llnc., Ridgeville,

Ind.

[22] Filed: Aug. 27, 1970 [21] Appl. No.: 67,307

Primary Examiner-Carroll B. Dority, Jr. Attorney-Ho0d, Gust, Irish & Lundy [5 7] ABSTRACT A gas burner of the type having a blast tube and a blower for supplying air to the blast tube adjacent its rear end. A gas and air mixing tube is longitudinally supported in the blast tube with its forward end spaced rearwardlly from the forward end of the blast tube, and a nozzle injects gas into the rear end of the mixing tube. The mixing tube has an air inlet opening adjacent its rear end for admitting primary air thereto for forward flow therein and mixture with the gas, the secondary air flowing forwardly over and around the mixing tube. The relationship of the primary and secondary airflow is controlled by a gate for selectively varying the area of the air inlet opening in the mixing tube. A burner drum is mounted in the forward end of the blast tube by a partition extending between the rear end of the drum and the forward end of the mixing tube, the drum extending longitudinally forwardly from the partition with its forward end spaced rearwardly from the forward end of the blast tube, the secondary air flowing forwardly over and around the drum and a flame being formed within the drum upon ignition of the fuel-air mixture exiting from the mixing tube. The drum has elongated, circumferentially extending slots formed in its wall forwardly of the mixing tube so that the secondary air flowing forwardly over the drum and the slots creates a partial vacuum adjacent the inner surface of the drum wall so as to spread the flame in the drum.

141 (Claims, 12 Drawing IIFigures SHEET 2 OF 6 MTENTEU m1 8 m2 BY ATTORNEYS,

PATENTED m 1 8 me SHEET 3 INVENTOF? PAUL D. Cox,

ATTORNEYS.

Pmgmmmwaasv 3.635.646

sum u or 6 FIG] INVENTQQ: PAUL D.Co

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GASBURNER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to fluid fuel burners, and more particularly to gas burners of the gun type.

2. Description of the Prior Art In US. Pat. No. 3,152,635 of the present inventor and William A. Cox, there is described and illustrated a gas burner incorporating a blast tube, a gas and air mixing tube extending longitudinally within the blast tube which receives primary air from the blower and into which the gas is injected for mixture with the primary air, a flame retention ring at the forward end of the mixing tube which comprises alternately inwardly and outwardly extending projections, and a drum surrounding the forward end of the mixing tube being spaced therefrom and from the blast tube, the forward end of the drum being aligned with the forward end of the mixing tube, and the mixing tube and drum including means for checking and deflecting the secondary airflow entering the drum.

In application Ser. No. 820,254 filed Apr. 29, 1969, now US. Pat. No. 3,552,897 of the present inventor, there is dis closed a gas burner of the general type shown in the aforesaid patent which incorporates a manually actuated flint-andstriker-wheel sparking device for igniting the pilot burner.

Gas burners of the general type described and illustrated in the aforesaid patent and application are used in a wide variety of applications, such as in warm air furnaces for mobile homes, incinerators, boilers, ovens, heat-treating systems, and radiant heating applications. It is desirable in the design of such gas burners that the burner be readily adjustable so as to provide a wide range of flame lengths from very short so as to permit use of the burner in small combustion chambers, to very long for radiant heating applications in which the flame is projected down an elongated tube. Further, such a gas burner must be readily adaptable for use with natural, mixed, manufactured or liquid propane gas.

SUMMARY OF THE INVENTION The invention, in its broader aspects, provides an improvement in a fluid fuel burner assembly of the type including an elongated blast tube having an open forward end and a rear end with means for supplying air under pressure to the blast tube adjacent its rear end. An elongated fuel and air mixing tube is provided having an open forward end and a rear end with means for supporting the mixing tube longitudinally within the blast tube in spaced, parallel relationship therewith and with its forward end spaced rearwardly from the forward end of the blast tube. Means are provided for injecting fluid fuel into the mixing tube adjacent its rear end, the mixing tube having an air inlet opening therein adjacent its rear end for admitting thereto a primary portion of the air supplied to the blast tube for flow toward the forward end of the mixing tube and mixture with the fuel injected therein, the remaining secondary portion of the air flowing toward the forward end of the blast tube over and around the mixing tube. Means are provided for selectively varying the area of the air inlet opening in the mixing tube thereby to vary the relationship of the primary and secondary air portions. The improvement includes a burner drum having an open forward end and a rear end, and a partition extending between the drum adjacent its rear end and the mixing tube adjacent its forward end for supporting the drum in spaced parallel relationship between the blast and mixing tubes with the drum extending longitudinally forwardly from the forward end of the mixing tube and having its forward end spaced rearwardly from the forward end of the blast tube, so that the secondary portion of the air flows forwardly over and around the drum and a flame is formed within the drum upon ignition of the fuel-air mixture exiting from the forward end of the mixing tube. The drum has at least one opening in its wall forwardly of the forward end of the mixing tube so that the secondary portion of the air flowing forwardly over the drum and the opening creates a partial vacuum ad- LII jacent the inner surface of the drum wall thereby spreading the flame in the drum. This arrangement permits a wide variation in the length of the flame from a very short flame with the air inlet opening in the mixing tube completely open, to a very long flame with the means for varying the area of the air inlet opening closing off a substantial portion of the air inlet opening thereby reducing the volume and velocity of the primary airflow within the mixing tube and increasing the volume and velocity of the secondary airflow over the drum.

In accordance with a further feature of the invention, means are provided for equalizing the pressure of the secondary air in the blast tube around the mixing tube.

It is accordingly an object of the invention to provide an improved fluid fuel burner.

Another object of the invention is to provide an improved fluid fuel burner of the gun type wherein the length of the flame may readily be adjusted from very short to very long.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. II is a side view of the improved fluid fuel burner assembly of the invention;

FIG. 2 is a rear view ofthe burner of FIG. ll;

FIG. 3 is a fragmentary cross-sectional view taken generally along the line 3-3 of FIG. 2;

FIG. 4 is a front end view taken along the line 4-4l of FIG.

FIG. 5 is a fragmentary top cross-sectional view taken generally along the line 5-5 of FIG. 3;

FIG. 6 is a fragmentary top cross-sectional view taken generally along the line 66 of FIG. 3;

FIG. 7 is a fragmentary top cross-sectional view taken generally along the line 7-7 of FIG. 3;

FIG. 8 is a fragmentary view in perspective showing the support for the pilot burner and sparking device pilot starting;

FIG. 9 is a fragmentary view in perspective further showing the pilot starter;

FIG. 10 is a fragmentary, enlarged end view of the burner;

FIG. 1 I is a view of the opposite side of the burner; and

FIG. I2 is a fragmentary cross-sectional view taken generally along the line I2-ll2 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1,2 and III of the drawings, there is shown a gun-type gas burner, generally indicated at 20 incorporating the improved construction of the invention. Burner 20 generally comprises a conventional blast tube 22 having a front end 24 and a rear end 26 closed by cover plate 28. A conventional mounting flange 30 is provided on blast tube 22 for securing burner 20 to the wall of the furnace or other device to be fired by the burner so that the forward end 24 of the blast tube is disposed within the fired device and the remaining components of the burner assembly are disposed outside of the device.

A conventional blower assembly 32 is provided having a casing 34 attached to blast tube 22 adjacent its rear end 26 and communicating therewith. Conventional impeller 34 (FIG. 12) is rotatably supported in blower casing MI and is driven in conventional fashion by motor 36. Referring additionally to FIG. 3 blower casing 34. terminates in air supply duct 38 attached to wall 40 of blast tube 22 adjacent rear end 26 and communicating with the interior of the blast tube for supplying air under pressure thereto from impeller 34, as shown by arrow 42. Damper plate 35 selectively adjusts the area of air inlet opening of blower 32.

An elongated gas and air mixing tube 44 is provided within blast tube 22 in spaced, parallel relationship therewith, mixing tube 44 being disposed on axis 46 eccentric with respect to axis 48 of blast tube 22. Mixing tube 44 has its forward end 46 spaced rearwardly from forward end 24 of blast tube 22, and has its rear end 48 secured to gas fitting 50, as by welding. Main gas inlet pipe 52 is attached to fitting 50 and communicates with cavity 54 therein. Gas inlet pipe 52 is coupled to conventional control unit 56 having gas supply line 58 coupled thereto. Control unit 56 includes main and pilot shutoff controls, a gas pressure regulator, the main gas valve, and an automatic pilot control (not shown).

Conventional nozzle 60 seated in cavity 54 of fitting 50 injects gas forwardly into the interior of mixing tube 44. Fitting 50 has a neck portion 62 projecting through opening 64 in cover plate 28. Bushing 66 is threaded into cavity 54 of fitting 50 and gas pressure check plug 68 is threaded into bore 70 in bushing 66. Cover plate 28 is removably secured to rear end 26 of blast tube 22 by threaded fasteners 29 (FIG.

Mixing tube 44 has an air inlet opening 72 formed in its wall adjacent rear end 48, opening 72 being aligned with air supply duct 38 and serving to admit primary air to mixing tube 44 for forward flow toward end 46 and mixture with the gas injected therein by nozzle 60. Gate sleeve 74 is slidably mounted on mixing tube 44 and is selectively adjustable longitudinally, thereby selectively to vary the area of air inlet opening 72, by means of arm 76 FIG. 7) which has a threaded portion 78 extending rearwardly through an opening 80 in cover plate 28. Adjusting and locking screws 82 engage threaded portion 78 of arm 76 on the exterior of cover plate 28. It will be readily seen that selective adjustment of the position of gate sleeve 74 thereby to vary the area of inlet opening 72 will vary the relationship between the volume and velocity of the primary air flowing forwardly in mixing tube 44 and volume and velocity of the secondary air flowing forwardly in blast tube 22 over and around mixing tube 44.

Burner head drum 84 is provided concentric with axis 48 of blast tube 22. Partition 86 connects rear end 88 of drum 84 to forward end 46 of mixing tube 44, drum 84 extending longitudinally forwardly from forward end 46 of mixing tube 44 with its forward end 90 being spaced rearwardly from forward end 24 of blast tube 22. It will now be seen that the secondary air flowing through blast tube 22 over and around mixing tube 44 will flow forwardly over and around the exterior surface of drum 84, as shown by the arrow 92.

Flame retention ring 94 is seated in forward end 46 of mixing tube 44 and has alternate inwardly and outwardly extending projections 96, 98 formed thereon at forward end 46, as best seen in FIG. 4. It will now be seen that upon ignition of the air-gas mixture exiting from forward end 46 of mixing tube 44, a flame will be formed within burner head drum 84.

A plurality of first circumferentially extending and circumferentially aligned slots 100 is formed in drum 84 adjacent forward end 46 of mixing tube 44, and a second plurality of circumferentially extending, circumferentially aligned slots 102 is formed in drum 84 between slots 100 and forward end 90. It will now be seen that as the secondary air 92 passes over and around the outer periphery of drum 84, and over slots 100, 102, a partial vacuum will be created adjacent the inner periphery of drum 84 which tends to pull the products of combustion radially outwardly, thereby spreading the flame, as indicated by the dashed lines 104. Provision of the openings or slots 100, 102 in burner head drum 84 makes possible the provision of a wide range of flame patterns and lengths, de pending upon the position of gate sleeve 74, from a very short, ultraviolet flame to a very long, radiant flame. Thus, with damper sleeve 74 adjusted so that air inlet opening 72 in mixing tube 44 is completely open, as shown in FIG. 3, the maximum volume and velocity of primary airflow is provided in mixing tube 44, and the minimum volume and velocity of secondary airflow is provided blast tube 22 and over burner head drum 84, thus providing minimum spreading of the flame and the shortest flame. As gate sleeve 74 is adjusted rearwardly thereby to reduce the area of air inlet opening 72, the volume and velocity of the primary airflow in mixing tube 44 is reduced while the volume and velocity of secondary airflow in blast tube 22 is increased, this increased velocity airflow over slots 100, 102 combined with the reduced volume and velocity of primary airflow in mixing tube 44 spreading and lengthening the flame.

It will be readily seen that it is important that the static pressure in blast tube 22 at all points around mixing tube 44 be generally equal in order to provide equal volume and velocity of airflow over and around burner head drum 84 so that the flame therein will be equally spread. Referring to FIGS. 3, 5 and 7, in order to provide equalization of the static pressures within blast tube 22 surrounding mixing tube 44, baffle plate 106 is provided disposed under rear end 48 of mixing tube 44. Baffle plate 106 has an opening 108 therein aligned with air supply duct 38 and air inlet opening 72 in mixing tube 44. Forward end 110 of baffle plate 106 is disposed forwardly of opening 72 and rear end 112 abuts cover plate 28. Baffle plate 106 extends transversely across blast tube 22 and has its side edges 114 closely spaced from wall 40 of blast tube 22, as at 116. Cutout portions or notches 118 are formed in the rear comers of bafile plate 106, as has been seen in FIGS. 5 and 7.

In the absence of baffle plate 106, the air entering blast tube 22 from supply duct 38 tends to flow initially upwardly around mixing tube 44 to the top of wall 40 with the result that the static pressure is higher in the upper portions of blast tube 22 over mixing tube 22 than in the lower portions under mixing tube 22. Baffle plate 106 tends initially to deflect a portion of the secondary air entering blast tube 22 forwardly under mixing tube 44, as shown by the dashed arrow 120, the remaining portion of the secondary air initially flowing upwardly through spaces 116 and cutout portions 118 into the upper portion of the blast tube over mixing tube 44, the result being general equalization of the static pressure of the secondary air in blast tube 22 around mixing tube 44.

Referring to FIGS. 3, 4, 6 and 9, ano'pening 122 is fonned in partition 86 below mixing tube 44 by folding up portion 124 thereof. Pilot burner housing 126 has its forward end 128 seated in opening 122. Housing 126 comprises bottom wall 130, top wall 132 and sidewalls 134, 136. Front end 138 of bottom wall abuts rear end 88 of drum 84, as best seen in FIG. 9. Partitions 140, 142 extend transversely across housing 126 and have aligned openings therein in which pilot burner 144 is supported, as best seen in FIGS. 3 and 6. Pilot burner 144 has its forward end 146 extending slightly into drum 84. Pilot burner 144 is coupled to control unit 56 by gas supply line 148 which extends rearwardly through blast tube 22, and external gas supply line 150 by fitting 149.

Flame detector 152 is also supported in housing 126 by partitions 140, 142 and is coupled to control unit 56 by sensing line 154. Drum 84 and the forward end of mixing tube 44 are supported in blast tube 22 by ears 137 and the bottom edges 139 of sidewalls 134, 136 of housing 126 which engage the inner surface of wall 40 of blast tube 22, as best seen in FIG. 4.

Referring to FIGS. 3, 4, 6, 8 and 9, a flint-and-striker-wheel sparking device 156 is provided of the type described and illustrated in my aforesaid application. Longitudinally elongated guideway 158 having an open rear end 160 is mounted on the bottom surface of bottom wall 130 of housing 126, forward end 162 of guideway 158 being adjacent rear end 88 of drum 84. Sparking device 156 comprises a transversely elongated member 164 formed by folding an elongated strip of metal upon itself, as at 166, as best seen in FIGS. 8 and 9. Slot 168 is formed in fold 166 and bearings 170 are fon'ned in one side of member 164 by crimping, bearings 170 rotatably receiving forward end 172 of elongated, rigid shaft 174. Striker wheel 176 is secured to forward end 172 of shaft 174 in slot 168. Longitudinally extending flint-receiving opening 178 is formed in member 164 by crimping, opening 178 communicating with slot 168 and striker wheel 176. A conventional flint 180 is seated in opening 178 and retained therein by conventional spring and screw assembly 182.

Side flanges 184 on guideway 158 slidably support member 164 for movement by shaft 174 between a forward position adjacent forward end 162 of guideway 1511, as shown in solid lines in FIG. 3, and a rear, inactive position, as shown in dashed lines at 1116. Forward end 138 of bottom wall 1311 has a cutout portion 186 formed therein which exposes striker wheel 176 of sparking device 156, when in its forward position, to pilot burner 1 11. Thus, manual rotation of shaft 1741 thereby to rotate striker wheel 176 against flint 1811 will provide sparks in opening 1611 which are in sufficiently close proximity to the forward end 1 16 of pilot burner 1411 to ignite the same.

Referring additionally to FIGS. 2 and 111, an elongated flexible shaft portion 198 has its forward end 2011 connected to rigid shaft 171 by connector 2112. A manual actuating knob 21141 is secured to rear end 2116 of flexible shaft 1%. An access opening 268 is formed in cover plate 211 through which sparking device 156 may be inserted and removed. Opening 21111 is normally closed by door 2111 mounted on cover plate 211 by hinge 212 and normally biased to its closed position by spring 21 1. When sparking device 156 has been inserted into blast tube 22 through opening 2118 and then seated in guideway 158, end 2116 of flexible shaft 1'98 extends through branch opening 216 formed in a side of opening 21111, branch opening 216 being exposed when door 2111 closes the remainder of opening 21111, as best seen in FIG. 2.

it will now be seen that sparking assembly 156 is manually inserted through opening 2118 and then manipulated by means of shaft 174i, 198 so as to insert it in guideway 1511, as shown by the arrow 2111 in FIG. 9, door 2111, when open, not only providing access for insertion and removal of sparking device 156, but also permitting observation thereof during its insertion into guideway 156, following which door 2111 may be closed. With end 2116 of flexible shaft 193 then seated in branch opening 216, sparking device 156 may be slidably moved forwardly in guideway 158 by means of shaft 174, 1911 to its forward, active position with striker wheel 176 exposed to opening 136 in bottom wall 1311 ofhousing 126, as shown in FIG. 3. When in this position, manual rotation of knob 211 1, which will be adjacent door 2111, will result in generation of sparks to ignite pilot burner 144. After burner 144 has been thus ignited, sparking device 156 may be slidably moved rearwardly by shaft 174, 1911 to its inactive position 1116.

An electric junction and control box 2211 is provided disposed over motor 36 and supported on blower casing 341 by wall 222 (FIG. 11). The rear sidewall 224 of control box 2211 is provided with a clip 226 which receives and retains end 2116 of flexible shaft 198 when the same is withdrawn so as to posi tion sparking device 156 in its inactive position 1116, end 2116 of flexible shaft 198 thus being bent at generally a right angle with respect to the remaining portion of the flexible shaft, as shown in dashed lines at 21160 in FIGS. 3.and 111.

Referring to FIGS. 2, 111, 11 and 12, the electrical control for burner 21), which may be of the type described and illustrated in my US. Pat. No. 3,245,456, is disposed in junction and control box 2211. External power supply leads 228 extend through the wall of control box 2211 and are connected to the control system therein. Leads 230 couple the control system in control box 2211 to blower motor 36. Armored cable 232 couples the control system to the control unit 56. Leads 231 couple a thermostat (not shown) to the control system in control box 2211.

Air'providing switch 236 forms a part of the electrical control for the burner and is disposed in box 2311 mounted on and depending from control box 2211 (FIG. 11). A vane 24 11 is pivotally mounted by shaft 212 in air supply duct 311 of blower casing 3 1. Vane 2 has a normal, at rest position, as shown in FIG. 12, resting against pin 244 when impeller 34 is not operating. Shaft 2 12 is journaled in the sidewalls of blower casing 3 1 and has an external lever 2416 connected thereto (FIG. 11). Airproviding switch 236 comprises a stationary contact 2 18 and a movable contact 2511, contacts 2 111, 2511 being normally open, as shown in FlG. 12. A pin 252 extends upwardly through opening 254 in box 2311 and opening 256 in insulating mounting board 258 of switch 236. Pin 252 is connected to lever member 2416 by pushrod 2611. It will readily be seen that operation of impeller 36 by motor 36 thereby discharging air under pressure in air supply duct 311, as shown by arrow 62, will result in pivotal movement of vane 22- 111 to the position shown in dashed lines at 2111a, thereby pivoting lever member 246 upwardly and actuating pushrod 2611 and pin 252 upwardly to engage movable contact: 2511 and move it upwardly into contact with contact 2 16.

While there have been described above the principles of this invention in connection with specific apparatus, it is to be clearly understood that this description made only by way of example and not as a limitation to the scope of the invention.

What is claimed is:

1. In a fluid fuel burner assembly comprising an elongated blast tube having an open forward end and a rear end, means for supplying air under pressure to said blast tube adjacent said rear end thereof, an elongated fuel and air mixing tube having an open forward end and a rear end, means for supporting said mixing tube longitudinally within said blast tube in spaced, parallel relationship therewith and with its forward end spaced rearwardly from said forward end of said blast tube, means for injecting fluid fuel into said mixing tube adjacent its rear end, said mixing tube having an air inlet opening therein adjacent its rear end for admitting thereto a primary portion of the air supplied to said blast tube for flow toward said forward end of said mixing tube and mixture with the fuel injected therein, the remaining secondary portion of said air flowing toward the forward end of said blast tube over and around said mixing tube, and means for selectively varying the area of said air inlet opening thereby to vary the relationship of said primary and secondary air portions; a burner drum having an open forward end and a rear end, a partition extending between said drum adjacent the rear end thereof and said mixing tube adjacent the forward end thereof for supporting said drum in spaced, parallel relationship between said blast and mixing tubes with said drum extending longitudinally forwardly from said forward end of said mixing tube and having its forward end spaced rearwardly from the forward end of said blast tube whereby said secondary portion of air flows forwardly over and around said drum and a flame is formed within said drum upon ignition of the fuel-air mixture exiting from the forward end of said mixing tube, said drum having at least one opening in its wall forwardly of said forward end of said mixing tube whereby said secondary portion air flowing forwardly over said drum and said opening creates a partial vacuum adjacent the inner surface of said drum wall thereby spreading the flame in said drum.

2. The burner of claim 1 wherein said opening comprises an elongated, circumferentially extending slot.

3. The burner of claim 1 wherein there are a plurality of said openings in said drum wall.

1. The burner of claim 3 wherein said openings comprise a first plurality of circumferentially aligned and extending, elongated slots adjacent said forward end of said mixing tube, and a second plurality of circumferentially aligned and extending, elongated slots intermediate said first slots and the forward end of said drum.

5. The burner of claim 1 further comprising a pilot burner extending through an opening in said partition into said drum.

6. The burner of claim 5 further comprising means mounted on said partition and extending rearwardly from said rear end of said drum for supporting said pilot burner in spaced, parallel relationship with said mixing tube.

7. The burner of claim 6 wherein said rear end of said blast tube is closed, and further comprising a fiint-and-strikingwheel sparking device, an elongated shaft having its forward end operatively connected to rotate the wheel of said device, means on the rear end of said blast for manually rotating the same thereby to rotate said wheel, and means for removably mounting said device on said supporting means in a position exposed to said pilot burner and with said shaft extending rearwardly through said blast tube and through an opening in said rear end thereof.

8. The burner of claim 7 wherein said mounting means comprises an elongated, longitudinally extending guideway having a forward end adjacent the rear end of said drum and an open rear end, said sparking device including a member slidably received in said guideway and longitudinally movable therein by said shaft between said exposed position and an inactive position spaced rearwardly therefrom, said shaft having a rigid portion connected to said wheel and a flexible portion terminating at said rear end thereof and projecting beyond said rear end of said blast tube in said inactive position of said device, and means on the exterior of said assembly for releasably retaining said flexible portion at an angle with respect to said rigid portion thereby to retain said device in said inactive position thereof.

9. The burner of claim 7 wherein said supporting means includes a plate member in spaced, parallel relationship with said mixing tube, said pilot burner being mounted on the side of said plate member facing said mixing tube, said mounting means being mounted on the side of said plate member remote from said mixing tube, said plate member having a front end adjacent the rear end of said drum, said front end of said plate member having an opening formed therein for exposing said sparking device to said pilot burner.

10. The burner of claim 7 wherein said supporting means comprises a housing having top, bottom and sidewalls, said housing having a forward end secured to said partition and seated in said opening therein, said bottom wall having a forward end closely adjacent said rear end of said drum, said housing extending rearwardly from said partition in parallel relationship with said mixing tube, and at least one transverse wall in said housing having an opening therein with said pilot burner extending therethrough; said mounting means comprising an elongated, longitudinally extending guideway mounted on the side of said bottom wall remote from said mixing tube and having a forward end adjacent the rear end of said drum and an open rear end, said sparking device including a member slidably received in said guideway and longitudinally movable therein by said shaft, said bottom wall having an opening therein adjacent said forward end thereof for exposing said sparking device to said pilot burner.

II. The burner of claim 1 wherein said air-supplying means includes an air supply duct opening through the wall of said blast tube, said mixing tube air inlet opening being formed in the wall thereof and being aligned with said air supply duct, and further comprising means in said blast tube for equalizing the pressure of the secondary portion of air therein around said mixing tube.

12. The burner of claim 11 wherein said equalizing means comprises a baffle plate between said blast tube and mixing tube and having an opening therein aligned with said air supply duct and air inlet opening, said baffle plate extending transversely across said blast tube and having side edges spaced from the wall thereof.

13. The burner of claim 12 wherein said rear end of said blast tube is closed, said baffle plate having a rear end closely adjacent said closed rear end of said blast tube and a forward end spaced forwardly from said air inlet opening, said baffle plate having cutout portions respectively formed in its corners defined by said rear end and side edges thereof.

14. The burner of claim 1 wherein said air-supplying means includes a blower casing having an exhaust portion communicating with said blast tube through the wall thereof, and an impeller in said casing; a vane in said exhaust portion, a shaft for pivotally mounting said vane for movement from a first to a second position in response to air supplied by said impeller, said shaft having a portion extending on the exterior of said casing, a switch having normally open contacts, and means operatively connecting said shaft extension portion to said switch for closing said contacts in response to movement of said vane to said second position. 

1. In a fluid fuel burner assembly comprising an elongated blast tube having an open forward end and a rear end, means for supplying air under pressure to said blast tube adjacent said rear end thereof, an elongated fuel and air mixing tube having an open forward end and a rear end, means for supporting said mixing tube longitudinally within said blasT tube in spaced, parallel relationship therewith and with its forward end spaced rearwardly from said forward end of said blast tube, means for injecting fluid fuel into said mixing tube adjacent its rear end, said mixing tube having an air inlet opening therein adjacent its rear end for admitting thereto a primary portion of the air supplied to said blast tube for flow toward said forward end of said mixing tube and mixture with the fuel injected therein, the remaining secondary portion of said air flowing toward the forward end of said blast tube over and around said mixing tube, and means for selectively varying the area of said air inlet opening thereby to vary the relationship of said primary and secondary air portions; a burner drum having an open forward end and a rear end, a partition extending between said drum adjacent the rear end thereof and said mixing tube adjacent the forward end thereof for supporting said drum in spaced, parallel relationship between said blast and mixing tubes with said drum extending longitudinally forwardly from said forward end of said mixing tube and having its forward end spaced rearwardly from the forward end of said blast tube whereby said secondary portion of air flows forwardly over and around said drum and a flame is formed within said drum upon ignition of the fuel-air mixture exiting from the forward end of said mixing tube, said drum having at least one opening in its wall forwardly of said forward end of said mixing tube whereby said secondary portion air flowing forwardly over said drum and said opening creates a partial vacuum adjacent the inner surface of said drum wall thereby spreading the flame in said drum.
 2. The burner of claim 1 wherein said opening comprises an elongated, circumferentially extending slot.
 3. The burner of claim 1 wherein there are a plurality of said openings in said drum wall.
 4. The burner of claim 3 wherein said openings comprise a first plurality of circumferentially aligned and extending, elongated slots adjacent said forward end of said mixing tube, and a second plurality of circumferentially aligned and extending, elongated slots intermediate said first slots and the forward end of said drum.
 5. The burner of claim 1 further comprising a pilot burner extending through an opening in said partition into said drum.
 6. The burner of claim 5 further comprising means mounted on said partition and extending rearwardly from said rear end of said drum for supporting said pilot burner in spaced, parallel relationship with said mixing tube.
 7. The burner of claim 6 wherein said rear end of said blast tube is closed, and further comprising a flint-and-striking-wheel sparking device, an elongated shaft having its forward end operatively connected to rotate the wheel of said device, means on the rear end of said blast for manually rotating the same thereby to rotate said wheel, and means for removably mounting said device on said supporting means in a position exposed to said pilot burner and with said shaft extending rearwardly through said blast tube and through an opening in said rear end thereof.
 8. The burner of claim 7 wherein said mounting means comprises an elongated, longitudinally extending guideway having a forward end adjacent the rear end of said drum and an open rear end, said sparking device including a member slidably received in said guideway and longitudinally movable therein by said shaft between said exposed position and an inactive position spaced rearwardly therefrom, said shaft having a rigid portion connected to said wheel and a flexible portion terminating at said rear end thereof and projecting beyond said rear end of said blast tube in said inactive position of said device, and means on the exterior of said assembly for releasably retaining said flexible portion at an angle with respect to said rigid portion thereby to retain said device in said inactive position thereof.
 9. The burner of claim 7 wherein said supporting means includes a plate member in spaced, pArallel relationship with said mixing tube, said pilot burner being mounted on the side of said plate member facing said mixing tube, said mounting means being mounted on the side of said plate member remote from said mixing tube, said plate member having a front end adjacent the rear end of said drum, said front end of said plate member having an opening formed therein for exposing said sparking device to said pilot burner.
 10. The burner of claim 7 wherein said supporting means comprises a housing having top, bottom and sidewalls, said housing having a forward end secured to said partition and seated in said opening therein, said bottom wall having a forward end closely adjacent said rear end of said drum, said housing extending rearwardly from said partition in parallel relationship with said mixing tube, and at least one transverse wall in said housing having an opening therein with said pilot burner extending therethrough; said mounting means comprising an elongated, longitudinally extending guideway mounted on the side of said bottom wall remote from said mixing tube and having a forward end adjacent the rear end of said drum and an open rear end, said sparking device including a member slidably received in said guideway and longitudinally movable therein by said shaft, said bottom wall having an opening therein adjacent said forward end thereof for exposing said sparking device to said pilot burner.
 11. The burner of claim 1 wherein said air-supplying means includes an air supply duct opening through the wall of said blast tube, said mixing tube air inlet opening being formed in the wall thereof and being aligned with said air supply duct, and further comprising means in said blast tube for equalizing the pressure of the secondary portion of air therein around said mixing tube.
 12. The burner of claim 11 wherein said equalizing means comprises a baffle plate between said blast tube and mixing tube and having an opening therein aligned with said air supply duct and air inlet opening, said baffle plate extending transversely across said blast tube and having side edges spaced from the wall thereof.
 13. The burner of claim 12 wherein said rear end of said blast tube is closed, said baffle plate having a rear end closely adjacent said closed rear end of said blast tube and a forward end spaced forwardly from said air inlet opening, said baffle plate having cutout portions respectively formed in its corners defined by said rear end and side edges thereof.
 14. The burner of claim 1 wherein said air-supplying means includes a blower casing having an exhaust portion communicating with said blast tube through the wall thereof, and an impeller in said casing; a vane in said exhaust portion, a shaft for pivotally mounting said vane for movement from a first to a second position in response to air supplied by said impeller, said shaft having a portion extending on the exterior of said casing, a switch having normally open contacts, and means operatively connecting said shaft extension portion to said switch for closing said contacts in response to movement of said vane to said second position. 